Maybe a stupid question, but is the app sending this encrypted voice over the cellular channel, or is it making a data connection independent of the phone? Als

Maybe a stupid question, but is the app sending this encrypted voice over the cellular channel, or is it making a data connection independent of the phone? Also, on a different point, if I were trying to eavesdrop on someone's conversation, I would probably just try to hack the microphone with a different / already loaded app...